A light diffusing element is widely used in illumination covers, screens for projection televisions, surface-emitting devices (for example, liquid crystal display devices), and the like. In recent years, the light diffusing element has been used for enhancing display quality of liquid crystal display devices and the like and for improving viewing angle properties, for example. As the light diffusing element, for example, there is proposed a light diffusing element in which fine particles are dispersed in a matrix such as a resin sheet (see, for example, Patent Literature 1). In such light diffusing element, most of incident light scatters forward (output plane side), whereas a part thereof scatters backward (incident plane side). As a result, there arise problems in that an amount of transmitted light becomes small, and a display screen has an insufficient contrast.
Further, along with the widespread use of the liquid crystal display device, applications of the light diffusing element are increasing, such as placing a light diffusing element on a forefront surface of a liquid crystal display device so as to enhance display quality of the liquid crystal display device, and using a light diffusing element in a reflection type liquid crystal display device. In such utilization forms, the light diffusing element may be placed on an inner side (liquid crystal cell side in the case of application to a liquid crystal display device) of a polarizer. However, the light diffusing element as described in Patent Literature 1 has large depolarization, and hence cannot be substantially utilized in such fields. Further, there is an attempt to combine polarized glasses with a liquid crystal display device to achieve a three-dimensional (3D) display. In this case, if a light diffusing element is applied to a polarizing plate on a viewer side so as to enhance display quality of the liquid crystal display device, the light diffusing element as described in Patent Literature 1 has large depolarization, and hence a polarization shutter function does not work completely with the polarized glasses to cause crosstalk (phenomenon in which a video to be originally recognized by only the right eye can also be recognized by the left eye, or a video to be originally recognized by only the left eye can also be recognized by the right eye). Thus, the light diffusing element cannot be utilized practically.
As means for suppressing the depolarization as described above, there has been proposed a light diffusing material obtained by self-fusing so-called gradient index (GRIN) fine particles, in which a refractive index changes continuously from a center portion of each of the fine particles toward its outside (see, for example, Patent Literature 2). However, in the light diffusing material of Patent Literature 2 obtained by self-fusing the GRIN fine particles, a film is liable to become uneven during fusion to make it difficult to form a uniform surface, resulting in insufficient optical uniformity. In addition, according to the technology of Patent Literature 2, gaps between the particles remain during fusion to form bubbles in many cases, and backscattering due to the bubbles becomes very large. Thus, a degassing step for removing the bubbles is required.